1. Field of the Invention
The present invention relates to an image pickup device and a method of producing the image pickup device, and particularly, to an image pickup device that has a light receiving element with a transparent plate provided on the light receiving surface thereof, and a method of producing such an image pickup device.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 62-67863 (for example, page 4 and FIG. 2) (below, referred to as “reference 1”), Japanese Laid-Open Patent Application No. 5-13738 (for example, pages 2, 3, and FIG. 1) (below, referred to as “reference 2”), and Japanese Laid-Open Patent Application No. 5-41506 (for example, page 3, and FIG. 3) (below, referred to as “reference 3”) disclose image pickup devices using a CCD or CMOS imaging sensor as an image pickup element (or, a light receiving element), in which the image pickup element is accommodated in a package, and a transparent glass plate is placed on the image pickup element to allow light outside to enter into the image pickup element through the glass plate.
In reference 1, a semiconductor substrate 21 is installed on a lead line 26, and an electrode of the semiconductor substrate 21 is connected to the lead line 26 through a bonding wire 25; a glass plate 22 is placed on the upper surface of the semiconductor substrate 21 (light receiving surface), and the semiconductor substrate 21, the lead line 26, the electrode of the semiconductor substrate 21, the bonding wire 25, and others are sealed by using a resin 23, which includes black pigment and functions as a light absorbing material, so that the surface of the glass plate 22 is exposed.
In reference 1, the sealing resin 23 is applied surrounding the glass plate 22 to seal the package. In the course of the sealing process, however, the sealing resin 23 may extend to the surface of the glass plate 22, that is, the light receiving surface, and may hinder entrance of light onto the semiconductor substrate 21, thereby resulting in reduction of the amount of light received by the light receiving element.
In reference 1, another embodiment is disclosed in which another glass plate 27 is arranged on the glass plate 22. In this structure, the glass plate 27 is situated on both of the glass plate 22 and the resin 23 and is bonded with the glass plate 22. In this structure, however, similar to the former embodiment, the resin 23 also flows to the surface of the glass plate 22, and this hinders entrance of light onto the semiconductor substrate 21, and results in reduction of the amount of light received by the light receiving element.
In reference 2, an on-chip lens 3 and a transparent glass plate 7 are provided on a solid image pickup element 2, with a space 9 between the transparent glass plate 7 and the on-chip lens 3, and a transparent resin 8 is applied to cover the transparent glass plate 7.
In this structure, because the transparent glass plate 7 is covered by the transparent resin 8, light absorption can hardly occur in the transparent resin 8. However, because the surface of the resin 8 is not even, but has fine depressions and projections thereon, the incident light is scattered and reflected, resulting in loss of the incident light.
In order to improve the flatness of the surface of the transparent resin 8 formed by molding, usually, it may be attempted to improve smoothness of the mold for molding the transparent resin 8 (in other words, to reduce roughness of the mold), or to grind the surface of the transparent resin 8 after molding. Due to these treatments, however, the cost of fabrication rises.
In reference 3, a micro-lens 4 and a glass plate 7 are provided on a solid image pickup element 1, with a transparent resin 5 between the glass plate 7 and the micro-lens 4, and a transparent resin 6 is applied to cover the glass plate 7.
In this structure, because the glass plate 7 is covered by the transparent resin 6, even when the resin 6 is extended, it does not hinder entrance of light into the light receiving element.
In order for the transparent resin to have a high light transmission characteristic, it is required that glass fibers or carbon granules or other fillers not be added in the transparent resin. Due to this, however, the thermal expansion coefficient of the transparent resin increases, and as a result, when sealing the package, or when the package is heated during mounting the package to an electronic device, the transparent resin may deform. Because of the deformation of the transparent resin, the semiconductor device also deforms, for example, the device bends, and this imposes large stresses on the glass plate 7, the micro-lens 4, and the solid image pickup element 1, thereby degrading the performance of the image pickup device.
Summarizing the problems to be solved, in the technique disclosed by reference 1, the sealing resin 23 is applied surrounding the glass plate 22 for sealing, but in the course of sealing, the sealing resin 23 may extend to the surface of the glass plate 22, which is the light receiving portion, and may hinder entrance of light onto the semiconductor substrate 21 and result in reduction of the amount of light received by the light receiving element.
Even when the additional glass plate 27 is arranged on the glass plate 22, as disclosed in another embodiment in reference 1, in which the glass plate 27 is situated on both of the glass plate 22 and the resin 23 and is bonded with the glass plate 22, the problems remain in that the resin 23 flows to the surface of the glass plate 22, hinders entrance of light onto the semiconductor substrate 21, and results in reduction of the amount of light received by the light receiving element.
In the technique disclosed in reference 2, because the transparent glass plate 7 is covered by the transparent resin 8, light absorption can hardly occur in the transparent resin 8, but because of the fine unevenness of the surface of the resin 8, the incident light is scattered and reflected, resulting in loss of the incident light.
In the technique disclosed in reference 3, in order for the transparent resin to have a high light transmission characteristic, it is required that glass fibers or carbon granules or other fillers not be added in the transparent resin. For this reason, the thermal expansion coefficient of the resin increases, and when sealing the package, or when the package is heated during mounting the package to an electronic device, the transparent resin may deform; this deformation may further induce deformation of the semiconductor device (for example, bending of the device), and further imposes large stresses on the glass plate 7, the micro-lens 4, and the solid image pickup element 1, thereby degrading the performance of the image pickup device.